The definition of a first name is the name that is given at birth.
An example of a first name is Brad in Brad Pitt's name.
the first of one's given names
A given name or the name that occurs first in a given name.
(plural first names)
- The first element of a full name.
- address the students by their first name from the first day on; we are not yet on a first-name basis
- attributive form of first name, noun.